package com.trilead.ssh2;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.security.SecureRandom;

import com.trilead.ssh2.channel.Channel;
import com.trilead.ssh2.channel.ChannelManager;
import com.trilead.ssh2.channel.X11ServerData;

/**
 * A <code>Session</code> is a remote execution of a program. "Program" means in
 * this context either a shell, an application or a system command. The program
 * may or may not have a tty. Only one single program can be started on a
 * session. However, multiple sessions can be active simultaneously.
 * 
 * @author Christian Plattner, plattner@trilead.com
 * @version $Id: Session.java,v 1.2 2008/03/03 07:01:36 cplattne Exp $
 */
public class Session {
	ChannelManager cm;
	Channel cn;

	boolean flag_pty_requested = false;
	boolean flag_x11_requested = false;
	boolean flag_execution_started = false;
	boolean flag_closed = false;

	String x11FakeCookie = null;

	final SecureRandom rnd;

	Session(ChannelManager cm, SecureRandom rnd) throws IOException {
		this.cm = cm;
		this.cn = cm.openSessionChannel();
		this.rnd = rnd;
	}

	/**
	 * Close this session. NEVER forget to call this method to free up resources
	 * - even if you got an exception from one of the other methods (or when
	 * getting an Exception on the Input- or OutputStreams). Sometimes these
	 * other methods may throw an exception, saying that the underlying channel
	 * is closed (this can happen, e.g., if the other server sent a close
	 * message.) However, as long as you have not called the
	 * <code>close()</code> method, you may be wasting (local) resources.
	 * 
	 */
	public void close() {
		synchronized (this) {
			if (flag_closed)
				return;

			flag_closed = true;

			if (x11FakeCookie != null)
				cm.unRegisterX11Cookie(x11FakeCookie, true);

			try {
				cm.closeChannel(cn, "Closed due to user request", true);
			} catch (IOException ignored) {
			}
		}
	}

	/**
	 * Execute a command on the remote machine.
	 * 
	 * @param cmd
	 *            The command to execute on the remote host.
	 * @throws IOException
	 */
	public void execCommand(String cmd) throws IOException {
		if (cmd == null)
			throw new IllegalArgumentException("cmd argument may not be null");

		synchronized (this) {
			/*
			 * The following is just a nicer error, we would catch it anyway
			 * later in the channel code
			 */
			if (flag_closed)
				throw new IOException("This session is closed.");

			if (flag_execution_started)
				throw new IOException("A remote execution has already started.");

			flag_execution_started = true;
		}

		cm.requestExecCommand(cn, cmd);
	}

	/**
	 * Get the name of the signal by which the process on the remote side was
	 * stopped - if available and applicable. Be careful - not all server
	 * implementations return this value.
	 * 
	 * @return An <code>String</code> holding the name of the signal, or
	 *         <code>null</code> if the process exited normally or is still
	 *         running (or if the server forgot to send this information).
	 */
	public String getExitSignal() {
		return cn.getExitSignal();
	}

	/**
	 * Get the exit code/status from the remote command - if available. Be
	 * careful - not all server implementations return this value. It is
	 * generally a good idea to call this method only when all data from the
	 * remote side has been consumed (see also the <code<WaitForCondition</code>
	 * method).
	 * 
	 * @return An <code>Integer</code> holding the exit code, or
	 *         <code>null</code> if no exit code is (yet) available.
	 */
	public Integer getExitStatus() {
		return cn.getExitStatus();
	}

	public InputStream getStderr() {
		return cn.getStderrStream();
	}

	public OutputStream getStdin() {
		return cn.getStdinStream();
	}

	public InputStream getStdout() {
		return cn.getStdoutStream();
	}

	/**
	 * This method can be used to perform end-to-end session (i.e., SSH channel)
	 * testing. It sends a 'ping' message to the server and waits for the 'pong'
	 * from the server.
	 * <p>
	 * Implementation details: this method sends a SSH_MSG_CHANNEL_REQUEST
	 * request ('trilead-ping') to the server and waits for the
	 * SSH_MSG_CHANNEL_FAILURE reply packet.
	 * 
	 * @throws IOException
	 *             in case of any problem or when the session is closed
	 */
	public void ping() throws IOException {
		synchronized (this) {
			/*
			 * The following is just a nicer error, we would catch it anyway
			 * later in the channel code
			 */
			if (flag_closed)
				throw new IOException("This session is closed.");
		}

		cm.requestChannelTrileadPing(cn);
	}

	/**
	 * Request authentication agent forwarding.
	 * 
	 * @param agent
	 *            object that implements the callbacks
	 * 
	 * @throws IOException
	 *             in case of any problem or when the session is closed
	 */
	public synchronized boolean requestAuthAgentForwarding(
			AuthAgentCallback agent) throws IOException {
		synchronized (this) {
			/*
			 * The following is just a nicer error, we would catch it anyway
			 * later in the channel code
			 */
			if (flag_closed)
				throw new IOException("This session is closed.");
		}

		return cm.requestChannelAgentForwarding(cn, agent);
	}

	/**
	 * Basically just a wrapper for lazy people - identical to calling
	 * <code>requestPTY("dumb", 0, 0, 0, 0, null)</code>.
	 * 
	 * @throws IOException
	 */
	public void requestDumbPTY() throws IOException {
		requestPTY("dumb", 0, 0, 0, 0, null);
	}

	/**
	 * Basically just another wrapper for lazy people - identical to calling
	 * <code>requestPTY(term, 0, 0, 0, 0, null)</code>.
	 * 
	 * @throws IOException
	 */
	public void requestPTY(String term) throws IOException {
		requestPTY(term, 0, 0, 0, 0, null);
	}

	/**
	 * Allocate a pseudo-terminal for this session.
	 * <p>
	 * This method may only be called before a program or shell is started in
	 * this session.
	 * <p>
	 * Different aspects can be specified:
	 * <p>
	 * <ul>
	 * <li>The TERM environment variable value (e.g., vt100)</li>
	 * <li>The terminal's dimensions.</li>
	 * <li>The encoded terminal modes.</li>
	 * </ul>
	 * Zero dimension parameters are ignored. The character/row dimensions
	 * override the pixel dimensions (when nonzero). Pixel dimensions refer to
	 * the drawable area of the window. The dimension parameters are only
	 * informational. The encoding of terminal modes (parameter
	 * <code>terminal_modes</code>) is described in RFC4254.
	 * 
	 * @param term
	 *            The TERM environment variable value (e.g., vt100)
	 * @param term_width_characters
	 *            terminal width, characters (e.g., 80)
	 * @param term_height_characters
	 *            terminal height, rows (e.g., 24)
	 * @param term_width_pixels
	 *            terminal width, pixels (e.g., 640)
	 * @param term_height_pixels
	 *            terminal height, pixels (e.g., 480)
	 * @param terminal_modes
	 *            encoded terminal modes (may be <code>null</code>)
	 * @throws IOException
	 */
	public void requestPTY(String term, int term_width_characters,
			int term_height_characters, int term_width_pixels,
			int term_height_pixels, byte[] terminal_modes) throws IOException {
		if (term == null)
			throw new IllegalArgumentException("TERM cannot be null.");

		if ((terminal_modes != null) && (terminal_modes.length > 0)) {
			if (terminal_modes[terminal_modes.length - 1] != 0)
				throw new IOException(
						"Illegal terminal modes description, does not end in zero byte");
		} else
			terminal_modes = new byte[] { 0 };

		synchronized (this) {
			/*
			 * The following is just a nicer error, we would catch it anyway
			 * later in the channel code
			 */
			if (flag_closed)
				throw new IOException("This session is closed.");

			if (flag_pty_requested)
				throw new IOException("A PTY was already requested.");

			if (flag_execution_started)
				throw new IOException(
						"Cannot request PTY at this stage anymore, a remote execution has already started.");

			flag_pty_requested = true;
		}

		cm.requestPTY(cn, term, term_width_characters, term_height_characters,
				term_width_pixels, term_height_pixels, terminal_modes);
	}

	/**
	 * Request X11 forwarding for the current session.
	 * <p>
	 * You have to supply the name and port of your X-server.
	 * <p>
	 * This method may only be called before a program or shell is started in
	 * this session.
	 * 
	 * @param hostname
	 *            the hostname of the real (target) X11 server (e.g., 127.0.0.1)
	 * @param port
	 *            the port of the real (target) X11 server (e.g., 6010)
	 * @param cookie
	 *            if non-null, then present this cookie to the real X11 server
	 * @param singleConnection
	 *            if true, then the server is instructed to only forward one
	 *            single connection, no more connections shall be forwarded
	 *            after first, or after the session channel has been closed
	 * @throws IOException
	 */
	public void requestX11Forwarding(String hostname, int port, byte[] cookie,
			boolean singleConnection) throws IOException {
		if (hostname == null)
			throw new IllegalArgumentException(
					"hostname argument may not be null");

		synchronized (this) {
			/*
			 * The following is just a nicer error, we would catch it anyway
			 * later in the channel code
			 */
			if (flag_closed)
				throw new IOException("This session is closed.");

			if (flag_x11_requested)
				throw new IOException("X11 forwarding was already requested.");

			if (flag_execution_started)
				throw new IOException(
						"Cannot request X11 forwarding at this stage anymore, a remote execution has already started.");

			flag_x11_requested = true;
		}

		/* X11ServerData - used to store data about the target X11 server */

		X11ServerData x11data = new X11ServerData();

		x11data.hostname = hostname;
		x11data.port = port;
		x11data.x11_magic_cookie = cookie; /*
											 * if non-null, then present this
											 * cookie to the real X11 server
											 */

		/*
		 * Generate fake cookie - this one is used between remote clients and
		 * our proxy
		 */

		byte[] fakeCookie = new byte[16];
		String hexEncodedFakeCookie;

		/* Make sure that this fake cookie is unique for this connection */

		while (true) {
			rnd.nextBytes(fakeCookie);

			/* Generate also hex representation of fake cookie */

			StringBuffer tmp = new StringBuffer(32);
			for (int i = 0; i < fakeCookie.length; i++) {
				String digit2 = Integer.toHexString(fakeCookie[i] & 0xff);
				tmp.append((digit2.length() == 2) ? digit2 : "0" + digit2);
			}
			hexEncodedFakeCookie = tmp.toString();

			/* Well, yes, chances are low, but we want to be on the safe side */

			if (cm.checkX11Cookie(hexEncodedFakeCookie) == null)
				break;
		}

		/* Ask for X11 forwarding */

		cm.requestX11(cn, singleConnection, "MIT-MAGIC-COOKIE-1",
				hexEncodedFakeCookie, 0);

		/* OK, that went fine, get ready to accept X11 connections... */
		/* ... but only if the user has not called close() in the meantime =) */

		synchronized (this) {
			if (flag_closed == false) {
				this.x11FakeCookie = hexEncodedFakeCookie;
				cm.registerX11Cookie(hexEncodedFakeCookie, x11data);
			}
		}

		/* Now it is safe to start remote X11 programs */
	}

	/**
	 * Inform other side of connection that our PTY has resized.
	 * <p>
	 * Zero dimension parameters are ignored. The character/row dimensions
	 * override the pixel dimensions (when nonzero). Pixel dimensions refer to
	 * the drawable area of the window. The dimension parameters are only
	 * informational.
	 * 
	 * @param term_width_characters
	 *            terminal width, characters (e.g., 80)
	 * @param term_height_characters
	 *            terminal height, rows (e.g., 24)
	 * @param term_width_pixels
	 *            terminal width, pixels (e.g., 640)
	 * @param term_height_pixels
	 *            terminal height, pixels (e.g., 480)
	 * @throws IOException
	 */
	public void resizePTY(int term_width_characters,
			int term_height_characters, int term_width_pixels,
			int term_height_pixels) throws IOException {
		synchronized (this) {
			/*
			 * The following is just a nicer error, we would catch it anyway
			 * later in the channel code
			 */
			if (flag_closed)
				throw new IOException("This session is closed.");
		}

		cm.resizePTY(cn, term_width_characters, term_height_characters,
				term_width_pixels, term_height_pixels);
	}

	/**
	 * Start a shell on the remote machine.
	 * 
	 * @throws IOException
	 */
	public void startShell() throws IOException {
		synchronized (this) {
			/*
			 * The following is just a nicer error, we would catch it anyway
			 * later in the channel code
			 */
			if (flag_closed)
				throw new IOException("This session is closed.");

			if (flag_execution_started)
				throw new IOException("A remote execution has already started.");

			flag_execution_started = true;
		}

		cm.requestShell(cn);
	}

	/**
	 * Start a subsystem on the remote machine. Unless you know what you are
	 * doing, you will never need this.
	 * 
	 * @param name
	 *            the name of the subsystem.
	 * @throws IOException
	 */
	public void startSubSystem(String name) throws IOException {
		if (name == null)
			throw new IllegalArgumentException("name argument may not be null");

		synchronized (this) {
			/*
			 * The following is just a nicer error, we would catch it anyway
			 * later in the channel code
			 */
			if (flag_closed)
				throw new IOException("This session is closed.");

			if (flag_execution_started)
				throw new IOException("A remote execution has already started.");

			flag_execution_started = true;
		}

		cm.requestSubSystem(cn, name);
	}

	/**
	 * This method blocks until certain conditions hold true on the underlying
	 * SSH-2 channel.
	 * <p>
	 * This method returns as soon as one of the following happens:
	 * <ul>
	 * <li>at least of the specified conditions (see {@link ChannelCondition})
	 * holds true</li>
	 * <li>timeout > 0 and a timeout occured (TIMEOUT will be set in result
	 * conditions)</a>
	 * <li>the underlying channel was closed (CLOSED will be set in result
	 * conditions)</a>
	 * </ul>
	 * <p>
	 * In any case, the result value contains ALL current conditions, which may
	 * be more than the specified condition set (i.e., never use the "=="
	 * operator to test for conditions in the bitmask, see also comments in
	 * {@link ChannelCondition}).
	 * <p>
	 * Note: do NOT call this method if you want to wait for STDOUT_DATA or
	 * STDERR_DATA and there are concurrent threads (e.g., StreamGobblers) that
	 * operate on either of the two InputStreams of this <code>Session</code>
	 * (otherwise this method may block, even though more data is available in
	 * the StreamGobblers).
	 * 
	 * @param condition_set
	 *            a bitmask based on {@link ChannelCondition} values
	 * @param timeout
	 *            non-negative timeout in ms, <code>0</code> means no timeout
	 * @return all bitmask specifying all current conditions that are true
	 */

	public int waitForCondition(int condition_set, long timeout) {
		if (timeout < 0)
			throw new IllegalArgumentException("timeout must be non-negative!");

		return cm.waitForCondition(cn, timeout, condition_set);
	}

	/**
	 * This method blocks until there is more data available on either the
	 * stdout or stderr InputStream of this <code>Session</code>. Very useful if
	 * you do not want to use two parallel threads for reading from the two
	 * InputStreams. One can also specify a timeout. NOTE: do NOT call this
	 * method if you use concurrent threads that operate on either of the two
	 * InputStreams of this <code>Session</code> (otherwise this method may
	 * block, even though more data is available).
	 * 
	 * @param timeout
	 *            The (non-negative) timeout in <code>ms</code>. <code>0</code>
	 *            means no timeout, the call may block forever.
	 * @return <ul>
	 *         <li><code>0</code> if no more data will arrive.</li>
	 *         <li><code>1</code> if more data is available.</li>
	 *         <li><code>-1</code> if a timeout occurred.</li>
	 *         </ul>
	 * 
	 * @throws IOException
	 * @deprecated This method has been replaced with a much more powerful
	 *             wait-for-condition interface and therefore acts only as a
	 *             wrapper.
	 * 
	 */
	@Deprecated
	public int waitUntilDataAvailable(long timeout) throws IOException {
		if (timeout < 0)
			throw new IllegalArgumentException("timeout must not be negative!");

		int conditions = cm.waitForCondition(cn, timeout,
				ChannelCondition.STDOUT_DATA | ChannelCondition.STDERR_DATA
						| ChannelCondition.EOF);

		if ((conditions & ChannelCondition.TIMEOUT) != 0)
			return -1;

		if ((conditions & (ChannelCondition.STDOUT_DATA | ChannelCondition.STDERR_DATA)) != 0)
			return 1;

		/*
		 * Here we do not need to check separately for CLOSED, since CLOSED
		 * implies EOF
		 */

		if ((conditions & ChannelCondition.EOF) != 0)
			return 0;

		throw new IllegalStateException("Unexpected condition result ("
				+ conditions + ")");
	}
}
